Transformation of Solar Disc Radiances into a Top of the Atmosphere Radiance Source for On-Orbit Solar Calibration of Terrestrial Radiance Measurements

Characteristics have been measured for a series of transmission optical devices that are considered for use in transforming solar disc radiances into a top of the atmosphere solar radiance source which can be used to calibrate terrestrial radiance measurements derived from orbiting remote sensing instruments. The types of transmission optical elements that were evaluated are a diffraction hole-plate, plates of fused silica and glass with ground surfaces, several types of microlens arrays and "engineered" diffusers. Collimated light from a diffuse source with approximately the angular solar diameter was imaged onto a CCD camera by a long focal length achromat at multiple narrow band wavelengths. The optical transform device was inserted into the beam of collimated radiation on the source side of the achromatic lens.